Certain gas turbine blades have shrouds at the outer extremity of the airfoil. The blade shrouds are typically designed with an interlocking feature, usually in the form of a notch, which allows each blade to be interlocked at its shroud with an adjacent neighbor blade when such blades are installed about the circumference of a turbine disk. This interlocking feature assists in preventing the airfoils from vibrating, thereby reducing the stresses imparted on the blades during operation.
Turbine blades are often made of nickel-based superalloys or other high temperature superalloys designed to retain high strength at high temperature. The material of the blade shrouds and the interlocking notch may lack sufficient hardness to withstand wear stresses and rubbing which occur during start-up and shut-down of a turbine engine, as the shrouded blades twist to an “interlocked” and “non-interlocked” position, respectively. Due to the relatively low Rockwell hardness of the typical materials of the blade shrouds and the interlocking notch, the interlocks may wear, resulting in gaps opening between the blade shrouds, thereby allowing the airfoils to twist and further deform, and even to possibly vibrate during operation which is highly undesirable as such imparts additional higher stresses on the blades which can quickly lead to blade breakage and consequent failure of the turbine.